CAPS: Cryopyrin-associated periodic syndromes

What is it?

CAP syndromes are autoinflammatory diseases that are usually inherited and include three different conditions with overlapping syndromes of increasing severity:[1]

Possible symptoms of CAPS (modified according to [3–5])

How common is it?

CAP syndromes are extremely rare, affecting about one person in every one million people.[2]

It is believed that there may be additional cases of CAPS that remain undiagnosed, or misdiagnosed. Further to this, some patients present with symptoms of more than one CAPS condition, complicating the differential diagnosis of FCAS, MWS or NOMID. [2]

What are the symptoms?

The severity and frequency of symptoms differs for each of the three conditions. Familial cold autoinflammatory syndrome (FCAS) is considered the mildest form and it is not associated with chronic inflammation, while neonatal-onset multisystem inflammatory disorder (known as the chronic infantile neurologic, cutaneous, and articular syndrome, NOMID/CINCA) is the most severe.[3]

Common symptoms of CAPS include hive-like rash, fatigue, headache, fever, joint pain and swelling, and red eyes.[4] Symptoms may be triggered by cold or changing temperature, stress, and exertion. The more severe CAP syndromes have various other symptoms, including hearing loss and, in the case of NOMID/CINCA, damage to the brain (see above diagram).[4]

What typically happens over the course of the illness?

Most CAPS patients have symptoms from birth. However, FCAS and Muckle-Wells syndrome (MWS) can also start later in childhood or adulthood.[5]

The impact on a person’s life varies according to the severity of the syndrome.[5]

All people with CAPS experience episodes of fever, rash, joint pain, and eye inflammation, which in FCAS are triggered by exposure to cold temperatures. However, with increasing disease severity, inflammation of other organs – and the resulting organ damage and disability – differs widely.[4] Hearing loss eventually develops in most MWS patients but in NOMID/CINCA, this is usually seen in the first decade of life. While the long-term outcome in FCAS is generally favourable, the impact of the disease in NOMD/CINCA patients can be significant. The disability seen in NOMID patients relates to the duration, extent, and severity of the inflammation. If untreated, this leads to permanent organ damage and disability including loss of vision, slowing of growth, loss of mobility and problems with learning and understanding.[4,6]

How is it caused?

In CAPS, chronic activation of an inflammatory response occurs as a result of a mutation in the NLRP3 gene (also called NALP3, and CIAS1), which carries the code for a protein responsible for the activity of a chemical called interleukin 1 beta (IL-1β), that promotes the inflammatory response. In CAPS, alteration in this gene leads to a continuous production of IL-1β and, therefore, to a heightened inflammatory response that affects the entire body.[4,6]